A fourth way of measuring temperature depends on the alteration in the electric conductivity of a metal, resulting from changes of temperature. On this principle rests the resistance thermometer, which is also made of platinum.

Platinum is much used for making the sparking plugs in explosion motors. The compressed mixture of gases is caused to explode by an electric spark generated between the two platinum points.

As the coefficient of expansion of platinum is about equal to that of glass, platinum wire can be melted in that material. The incandescent-light factories make extensive use of it for this reason. The weight of the two wires used amounts to only a few milligrams, but their production in the aggregate places the incandescent-light factories among the principal consumers of platinum.

The consumption of platinum in the manufacture of artificial teeth is even greater. Platinum is used for this purpose because its coefficient of expansion is about equal to that of the tooth structure.

By reduction of the platinum salts solution platinum is obtained as a very finely separated, black powder, the so-called "platinum black." In this state platinum has the property of accelerating chemical reactions among gases without itself being affected. Thus, hydrogen and oxygen, for instance, will not combine at an ordinary temperature; but if the two gases are passed into rather finely divided platinum the latter glows, and the hydrogen and oxygen unite into water. It is owing to this property that the heated platinum point of the pyrographic apparatus is brought to a glow by the inrush of the mixture of benzine and air.

The most important industrial use of platinum catalysis is found in the sulphuricacid industry. Sulphuric acid is made of sulphuric dioxide, oxygen, and steam: SO2+O+H2O=H2SO,. Now, the SO, does not directly unite with O, and use is made in the lead-chamber processes of nitric acid as an oxidizing agent. In the year 1878 Clemens Winkler discovered that the two gases react if they are conducted at high temperature over finely divided platinum. From the discovery of this fact to its practical utilization was a long road, which can not be here followed through all its windings. Suffice it to say that the reaction was finally made industrially available, and to-day more than half of the sulphuric acid is made by the contact process.

The foregoing statement of the uses of platinum is limited to a description of the more important fields of its usefulness. Not only the platinum metals themselves, but also many of their salts, find technical utilization. Thus, barium platino-cyanide is used for making the well-known light shade for the Röntgen apparatus; great quantities of potassium platino-chloride are used in photography for making platinum types, and the ceramic art employs the salts of all platinum metals in making fireproof colors. Reliable figures on the consumption of platinum in the individual industries are not available. The development of electrical technics entails a steadily growing consumption; the use of platinum for jewelry has increased enormously in recent years, but is dependent on fashion, and therefore may quickly decline. The great revolution in the sulphuric-acid industry makes itself decidedly felt in the platinum business. The quantity of platinum used for artificial teeth is astonishingly large, amounting to about one-third of the total consumption—that is, to about 2,000 kilograms a year. This quantity of platinum is necessarily almost lost to the industry. And the case is the same with the greater part of the platinum used in the electrical industry. It never occurs to anyone to detach the little platinum plates on an old electric bell, because they are worth only a penny or two, and even getting the platinum from old incandescent lights is not very profitable. Only about a third of the metal used for this purpose finds its way back to the melting pot as old platinum; the remainder has always to be supplied new.

CADMIUM.

By C. E. SIEBENTHAL.

INTRODUCTION.

The chief output of cadmium comes from the zinc producing regions of Silesia, where it is recovered in zinc smelting. During the last two years cadmium has been produced in the United States. The zinc ore of the Joplin district averages fully as high in cadmium as the cadmium-bearing zinc ores of Silesia. For this reason, and because of the increasing use of this metal in art and industry, the following short account of the metal is given.

PRODUCTION.

Cadmium has been produced in the United States since 1907 by the Grasselli Chemical Company, of Cleveland, Ohio. The metal is recovered, according to various accounts in the technical journals, as a by-product in the fractional distillation of zinc ores, but of this there has been no official confirmation. Inasmuch as the production is confined to one firm, the quantity and value of the output can not be given. That it does not fall far short of supplying the domestic demand, however, is to be inferred from the sudden fall in the value of cadmium imports for consumption, as given on a later page.

PRODUCTION IN GERMANY.

The following table gives the production of cadmium in Upper Silesia from 1882 to 1908, inclusive:

Quantity and value of cadmium produced in Germany, 1882-1908.a

a Recalculated to pounds and dollars from Statistik des Oberschlesischen Berg-und Hüttenmännischen Vereins, as quoted by Jensch, from Vierteljahreshefte zur Statistik des Deutschen Reichs and from Statstisches Jahrbuch fur den Preussischen Staat.

793

1895.

1896

1897

1898.

1899

1900.

1901

1902.

1903.

1904.

1905.

1906.

1907

1908.

Quantity and value of cadmium produced in Germany, 1882-1908-Continued.

Cadmium is imported into the United States as metallic stick cadmium and as the pigment, cadmium sulphide (CdS), cadmium yellow. The former is free of duty, while the latter is dutiable at 30 per cent ad valorem. The value of the imports for consumption of metallic cadmium for 1903 to 1908, inclusive, is given in the table below, which is taken from the records of the Bureau of Statistics. The quantities are not there recorded, and they have accordingly been computed by dividing the values of the imports by the average price of cadmium for the corresponding years in Silesia, from which country the cadmium was imported. The quantity of cadmium imported as a pigment and the value thereof are not kept separately by the Bureau of Statistics.

Cadmium imported for consumption into the United States, 1903–1908, in pounds.

The principal cadmium mineral is the sulphide, greenockite (CdS), but no deposits of this mineral have as yet been discovered which reach such volume as to be called cadmium ore. Deposits of greenockite are known at Bishoptown, Scotland; at Przibram, Bohemia; and at Neu-Sirka, Transylvania.

In the Joplin district crystals of blende occurring in pockets or crevices are often coated with a greenish-yellow deposit of greenockite. This is a secondary deposition or enrichment caused by the decomposition of cadmium-bearing blende in the superficial part of the ore body and the precipitation of the cadmium as sulphide at lower points. In no case known to the writer does this amount to more than a mere coating, which easily rubs off.

CADMIUM-BEARING ZINC ORES.

The chief source of cadmium the world over is cadmiferous zinc ore, sulphide, silicate, or carbonate, as the case may be. Lead ores likewise contain some cadmium, but not so commonly and in less quantity than zinc ore. Cadmium is reported in flue dust from Colorado lead smelters and in dust from lead-ore roasting furnaces at Freiberg, Germany. The oxidized zinc ores, smithsonite and calamine, generally carry a higher percentage of cadmium than does the blende in the same vicinity. Jensch has noted that the works on metallurgy give the cadmium content of Upper Silesia zinc ores as 2 to 5 per cent, and that this refers to the upper, shallower ores which have now been exhausted. He gives a large number of analyses of zinc ores, as mined more recently, of which few show more than three-tenths of 1 per cent of cadmium, and the average of all of which gives 0.102 per cent of cadmium. He also gives analyses of blendes and calamines from other parts of Europe which are being mined at present, and these also rarely contain more than three-tenths of 1 per cent of cadmium.

In South America zinc blende is reported from Morro do Bule, Ouro Preto, Brazil, which contains 2.4 per cent of cadmium, as well as 0.52 per cent of arsenic and 3.89 ounces of silver to the ton. It is found in vein formation in limestone.

In the United States, also, cadmium is found in the zinc ores. The • zinc ores of the Eastern States, with the exception of blende from Eaton, N. H., and Friedensville, Pa., have not been reported as cadmium bearing, though doubtless for the most part they carry small quantities of the metal. The ores of the upper Mississippi Valley are comparatively free from cadmium, so far as analyses are available. The zinc ore of the Kentucky-Illinois fluorspar district contains considerable cadmium and secondary deposition of greenockite has been noted as common. In the table of analyses which follows on a later page two analyses are given of blendes from this district, one from Illinois and one from Kentucky, both of which show small percentages of cadmium. No analyses of calamines showing the cadmium content are available from this district.

с

The Joplin district shows a comparatively large percentage of cadmium, the average of nearly 11,000 shipments, mostly carload lots, as shown in the table below being 0.358 per cent. This table of analyses of blendes from the Joplin district is quoted largely from an article by Prof. W. George Waring. Two additional analyses of composite samples made by the same authority in 1904 are also

included.

On the assumption that Joplin blende contains an average of 0.358 per cent of cadmium, as indicated by the table, the total cadmium content of the 236,860 short tons of zinc blende produced in the Joplin region in 1908 must have amounted to about 1,700,000 pounds of cadmium, over twenty times the production or consumption of cadmium in the world in 1908. About 85 per cent of the cadmium content of the ore is lost in the roasting and the fractional distillation. Nevertheless, the Joplin district could furnish annually three

a Sammlung chem. und chem.-tech. Vorträge, vol. 3, 1898, p. 202. Annaes da Escola de Minas de Ouro Preto, 1906, No. 8, pp. 17-22.

e Ulrich, E. O., and Smith, W. S. Tangier, The lead, zinc, and fluorspar deposits of western Kentucky: Prof. Paper U. S. Geol. Survey No. 36, 1905, p. 36.